The primary use for sputtering magnetrons is to sputter material from a target to deposit the target material on a deposition substrate. Fundamentally speaking, sputter deposition stems from a direct current glow discharge (i.e., plasma discharge) between an anode and a cathode in a vacuum. A neon sign is a simple example of such a direct current glow discharge. For sputtering, the cathode is a composed of a target material for which an incident ion knocks loose a target material atom. The target material atom then sticks to whatever surface it strikes. Sputtering a uniform layer of target material on a substrate requires a high level of target material atom scattering. However, such heightened scattering mandates a higher rate of target material consumption and requires frequent deposition chamber cleaning.
Though available in a number of geometries, magnetrons all function based on crossed E and B fields. Such an arrangement can be used to trap the plasma and steer the sputter deposition versus the unconstrained scattering introduced above. A magnetron is generally composed of one magnetic pole surrounding another magnetic pole. The arrangement creates an arched magnetic field between the poles in the shape of a tunnel. Electrons gyrate about lines of magnetic force and, when a continuous magnetic tunnel is present to prevent escape, they will drift along the tunnel until they recombine with an ion, or collide with an atom to form more charged particles. The positively charged ions thus created are drawn to the negative potential of the target where they bombard the target (or any negatively charged system component) to release more atoms. The benefit of using a sputtering magnetron (and the tunnel it produces) is a substantial increase in the sputtering rate coupled with reduced target material waste from deposition on surfaces other than the intended substrate surface.
The shape of the electron tunnel is described by the tangential magnetic flux pattern. These fields have been referred to as having “apple”, “bean”, “heart”, etc., shapes in the prior art. When used with ferrous materials, these field shapes are shunted extensively by the permeable target, so only thin targets allow the characteristic field shape of the magnetron to penetrate, contrary to the target required for a commercially practicable, thick deposition.
Rotating sputtering magnetrons are used, among other applications, to coat the data disks for hard disk drives. Current hard drive technology is based on linear recording. The next generation of hard drives will use vertical recording. This requires a thick deposition of highly magnetically permeable materials. Currently available rotating sputtering magnetrons neither have the field strength required to develop the necessary tangential magnetic field intensity at the surface of usably thick ferrous magnetic targets, nor the field shape needed to sweep the target surface uniformly to maximize target life.
The inability to use thick targets further contributes to the amount of maintenance required of a sputter deposition system. Given that the sputter depositions occur under vacuum and that any contamination contributes detrimentally to the quality of the sputtered material, it is extremely important that the deposition chambers of such systems are properly cleaned, qualified, and maintained. Not only does the use of thicker targets enable thicker depositions, but it also increases the lifespan of the target. The increased lifespan in turn increases the possible utilization of the machine (e.g., up-time versus maintenance down-time to replace the target and perform related maintenance tasks).